I'd have been horrified if they had stopped at season eight. They did tons of brilliant stuff after that, including Homer's Enemy, arguably the funniest episode of the show.
Uh, "Homer's Enemy"
was in season 8. People blame Mike Scully for the show's decline because it started to falter in season 9 when he took over, but I think it was doomed at that point no matter who took over. Few shows can stay fresh even after five seasons. That "The Simpsons"
maintained such a high degree of quality after 8 was an amazing achievement and the creators of the show should have quit while they were ahead, but they got greedy.